I have YP-U5AB with 1.51 firmware and there is a problem with turning it on. When it is turned off for a while and I press the power button to turn it on, it doesn't turn on right a way. If I wait for like 30 seconds and then try to turn it on, this time it turns on. It only does this when it stays turned off for a while. Any solutions? Thanks!!

Same issue here, on a U5 with 1.33 firmware.
Sometimes -randomly as it seems- it won't react to power button for 1-2 mins, then it powers on; other times it behaves the way it should.
Have tried with full, half-full and empty memory/battery, nothing changes.
Other people experiencing this?